What are the CURB65 (Confusion, Urea, Respiratory rate, Blood pressure, age 65) criteria for assessing pneumonia severity?

CURB-65 Criteria for Pneumonia Severity Assessment

What is CURB-65?

CURB-65 is a 5-point clinical scoring system that predicts mortality risk in community-acquired pneumonia by assigning one point each for: Confusion, Urea >7 mmol/L (or BUN ≥20 mg/dL), Respiratory rate ≥30 breaths/min, Blood pressure (systolic <90 mmHg or diastolic ≤60 mmHg), and age ≥65 years. 1, 2

The Five Components

Each criterion receives one point if present 1, 2:

• C - Confusion: New disorientation to person, place, or time, or altered mental status based on a specific mental test 1, 2
• U - Urea: Blood urea nitrogen (BUN) ≥20 mg/dL or urea >7 mmol/L 1, 2
• R - Respiratory rate: ≥30 breaths per minute 1, 2
• B - Blood pressure: Systolic <90 mmHg OR diastolic ≤60 mmHg 1, 2
• 65 - Age: ≥65 years 1, 2

Note: Systolic blood pressure is the best hemodynamic predictor; diastolic pressure may be neglected in some applications. 1

Risk Stratification and Mortality Prediction

The total score ranges from 0-5 points, with corresponding mortality risks 1, 2:

• Score 0-1: 0.7-2.1% mortality risk (low risk) 1, 2
• Score 2: 9.2% mortality risk (moderate risk) 1, 2
• Score 3: 14.5% mortality risk (high risk) 1, 2
• Score 4-5: 40-57% mortality risk (very high risk) 1, 2

Clinical Decision-Making Algorithm

For site-of-care decisions, use the following approach 1, 2:

• Score 0-1: Consider outpatient treatment (except if age ≥65 is the only criterion met, then hospitalization should be seriously considered) 1, 2
• Score 2: Consider short hospital stay or supervised outpatient treatment; clinical judgment is particularly important in this intermediate risk group 1, 2
• Score ≥3: Hospital admission required; assess for ICU admission 1, 2
• Score 4-5: Hospital admission with strong consideration for ICU-level care 1, 2

When to Override the Score

CURB-65 must be used as an adjunct to clinical judgment, not as the sole determinant. 2 Consider hospitalization regardless of score when 2:

• Septic shock requiring vasopressors (direct ICU admission)
• Acute respiratory failure requiring intubation/mechanical ventilation (direct ICU admission)
• Homelessness, psychiatric illness, or inability to take oral medications
• Lack of social support or inability to ensure medication adherence
• Comorbidity exacerbations (pneumonia worsening underlying conditions like heart failure or COPD)
• Failure of outpatient antibiotic therapy

Advantages of CURB-65

CURB-65 is preferred for its simplicity and practicality 1, 2:

• Uses only 5 easily remembered variables 1, 2
• Requires only one laboratory test (urea/BUN), readily available in most hospitals 2
• Can be calculated quickly in busy emergency departments without scoring sheets 1
• Helps reduce unnecessary hospitalizations while ensuring appropriate care for higher-risk patients 2

CRB-65: The Simplified Version

CRB-65 omits the urea measurement and can be used when laboratory testing is unavailable, giving a score range of 0-4 points 1, 2. This variant is particularly useful in 2:

• Primary care practitioner offices
• Outpatient settings
• Resource-limited environments

Important Limitations and Pitfalls

CURB-65 has specific populations where it may underestimate severity 2, 3:

• Young patients (<65 years) with severe respiratory failure: The score may underestimate severity in previously healthy patients under 65 with significant physiologic derangement, as age is heavily weighted 2, 3
• Elderly patients with comorbidities: May underestimate risk in patients with multiple comorbid conditions 2, 3
• Patients with baseline renal insufficiency: The urea criterion may be less reliable 1
• Nursing home-acquired pneumonia: CURB-65 performs poorly in this population; even CRB-80 fails to identify low-risk patients (22.75% mortality in "low-risk" group) 4

For ICU admission decisions specifically, CURB-65 performs less effectively than the IDSA/ATS severe CAP criteria, which should be used instead for ICU triage 2, 3. Direct ICU admission criteria include 2:

• ≥3 minor criteria for severe CAP
• Septic shock requiring vasopressors
• Acute respiratory failure requiring mechanical ventilation
• ≥2 of: systolic BP <90 mmHg, severe respiratory failure, multilobar involvement, or need for mechanical ventilation/vasopressors

Comparison with PSI

While both CURB-65 and the Pneumonia Severity Index (PSI) are validated tools, they have different strengths 1:

• PSI is more complex (20 variables) but may classify slightly more patients as low-risk with similar mortality rates 1
• CURB-65 is simpler and more practical in emergency settings 1, 2
• PSI requires scoring sheets or computerized decision support; CURB-65 is easily remembered 1
• Recent meta-analysis suggests CURB-65 has slightly better sensitivity (96.7%) and specificity (89.3%) for predicting ICU admission needs 5
• Both tools have been shown to be comparable in predicting mortality 1

Implementation Best Practices

To optimize CURB-65 use in clinical practice 2:

• Implement as part of a systematic pneumonia care bundle
• Always combine with clinical assessment of severity (tachypnea, tachycardia, hypotension, confusion) 1
• For patients with CURB-65 ≥3, promptly evaluate for potential ICU admission 2
• Consider comorbidities such as HIV, diabetes, heart failure, moderate-to-severe COPD, liver disease, renal disease, or malignancy when making final decisions 1, 2
• Expect clinical improvement within 3 days; patients should contact their physician if no improvement occurs 2